drm/amd/display: Allow individual control of eDP hotplug support

[Why]
Second eDP can send display off notification through HPD
but DC isn't hooked up to handle. Some primary eDP panels
will toggle on/off incorrectly if it's enabled generically.

[How]
Extend the debug option to allow individually enabling hotplug
either the first eDP or the second eDP in a dual eDP system.

Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Derek Lai <Derek.Lai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>